Multi-network operation for multicast groups

ABSTRACT

Techniques for bridging communication between multiple networks to facilitate distribution of multicast data are described herein. For example, the techniques may identify a particular node that is able to communicate with each network and instruct the particular node to act as a bridge between the networks. The particular node may forward data from either network to the other network. This may allow data for a multicast group to be distributed to members of the multicast group that are located in separate networks.

BACKGROUND

Nodes are often configured in a tree-like network structure, such as aDestination Oriented Directed Acyclic Graph (DODAG) with parent nodes,child nodes, and a root node. In many instances, a node belongs to oneDODAG, and one network (e.g., one Personal Area Network (PAN)) at agiven moment in time. The nodes often communicate multicast data to eachother through the DODAG. For example, a node will forward multicast datadestined for members of a multicast group upwards in the networknode-by-node to reach a root node. The root node will then distributethe multicast data back down into the network node-by-node to reach themembers of the multicast group. This results in a relatively largenumber of communications, often between nodes that are not members ofthe multicast group, ultimately causing network congestion. When thenodes are battery-powered, this increases battery consumption.

In addition, in many instances, nodes of separate networks (and separateDODAGs) belong to the same multicast group. Since the nodes are onlyconfigured to communicate within their own networks (e.g., intra-PANcommunication), this results in members of a multicast group notreceiving multicast data.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

FIG. 1 is a schematic diagram of an example network architecture.

FIG. 2 is a diagram showing details of an example network communicationdevice.

FIG. 3A illustrates an example network of nodes before formation of aPoint-to-Multipoint Sub-Tree (PST).

FIG. 3B illustrates an example network of nodes with indicatorsregarding a PST.

FIG. 4A illustrates example networks before a communication bridge hasbeen established.

FIG. 4B illustrates example networks after establishing a communicationbridge.

FIG. 5 illustrates an example process to form a PST and/or distributedata according to the PST.

FIGS. 6A-6B illustrate an example process to bridge communicationbetween multiple networks to facilitate distribution of multicast data.

FIG. 7 illustrates an example portion of a subscription message toadvertise that a node is a member of a multicast group.

FIG. 8 illustrates an example portion of a message to instruct a node todisable or enable a pruning state.

FIG. 9 illustrates an example process to bridge communication betweennetworks with a member node acting as a bridge.

FIG. 10 illustrates an example process to bridge communication betweennetworks with a member in an adjacent network.

FIG. 11 illustrates an example process at a root node to bridgecommunication between networks.

DETAILED DESCRIPTION

As discussed above, multicast communication within a tree-like networkoften requires a large number of communications to reach members of amulticast group. This causes network congestion and can consume batterypower. In addition, since a node is only configured to communicatewithin its own network (e.g., intra-PAN communication), and members of amulticast group are often in several networks, this results in membersof a multicast group not receiving multicast data.

This disclosure describes, in part, techniques directed to limitingforwarding of multicast communications. For example, the techniquesintelligently forward multicast data along paths of a network wheremembers of a multicast group are located. As such, nodes that do notlead to members of the multicast group may be pruned from distributionof the multicast data. This reduces network communications, ultimatelyconserving processing, communication, and/or battery resources of thenodes.

The techniques may be implemented in the context of a hierarchal networkstructure, such as a tree. Each node of the network may be connectedwirelessly and/or wired to a parent node and/or child node. Each nodemay be associated with a hierarchical level, with a root node beingassociated with the highest level. As communications are sent upward inthe network (i.e., uplink—from parent-to-parent), the communicationstravel closer to the root node. Meanwhile, as communications are sentdownward in the network (i.e., downlink—from child-to-child), thecommunications travel farther from the root node.

In one illustration, the techniques may form a Point-to-MultipointSub-Tree (PST) for a multicast group to limit unnecessary dataforwarding. The PST may be formed as nodes subscribe and/or unsubscribeto the multicast group. A node may subscribe to (i.e., join) themulticast group by sending a subscription message to advertisemembership in the multicast group. The subscription message may betransmitted node-by-node up the network to a root node. The path orchain of nodes from the node originating the subscription message to theroot node may form a forwarding chain. Each node that receives asubscription message may view the subscription message to maintain acount of child nodes from which the node has received a subscriptionmessage for a particular multicast group (also referred to as childcount of received subscriptions).

Each node of the network may also maintain a pruning state indicatingwhether or not to forward data for a multicast group. When the pruningstate is enabled, a node will generally not forward on multicast data,unless another condition is satisfied, such as being a common ancestor.In contrast, when the pruning state is disabled, the node will forwardmulticast data.

As part of forming the PST, the techniques may disable or enable apruning state by sending a message (sometimes referred to as a“Member-in-Path (MinP)” message) to a node instructing such change. Inone example, a parent node sends a message to a child node to disablethe child's pruning state when the parent node has received asubscription message for a multicast group from two or more differentchild nodes. The message may be sent downward along nodes of aforwarding chain to disable the pruning state of the nodes along theforwarding chain. Here, the parent node may be referred to as a “commonancestor,” since it has members in two or more branches. This may allowmulticast data to be forwarded from one branch to another branch (i.e.,from a child in one branch to a child in another branch).

In another example of updating a pruning state, a parent node sends amessage to a child node to disable the child's pruning state when theparent node is a member of a multicast group and is located on aforwarding chain for the multicast group. The message may be sentdownward along nodes of a forwarding chain to disable the pruning stateof the nodes along the forwarding chain. Here, the parent node may bereferred to as a “member ancestor” or a “member-in-path,” since theparent node is a member along a path to the root node (e.g., the parentmember is located on a forwarding chain established for another member).This may allow multicast data that originates in a member in a lowerlevel to be distributed to a member in a higher level, and vice versa.

The PST may be used to limit distribution of multicast data within thenetwork. In particular, the techniques may limit forwarding of multicastdata to branches that lead to members of a multicast group. For example,the techniques may prune a forwarding chain to limit unnecessary dataforwarding. In many instances, multicast data for a multicast group maybe forwarded from a node (either upwards or downwards in the network) ifa pruning state is disabled for the node for the multicast group and/orif a child count of received subscriptions for the multicast group istwo or greater (e.g., the node is a common ancestor). This mayintelligently distribute the multicast data along paths where members ofthe multicast group are located.

This disclosure also describes techniques directed to bridgingcommunication between multiple networks to facilitate distribution ofmulticast data. As noted above, in many instances nodes of separatenetworks (and separate DODAGs) belong to the same multicast group. Inorder to distribute multicast data to the members of the multicast groupthat span multiple networks, the techniques identify a particular nodethat is able to communicate with a node from each network and instructthe particular node to act as a bridge between the networks. Theparticular node may become a virtual member of the multicast group andforward multicast data from either network to the other network. Thismay allow multicast data for a multicast group to be distributed tomembers of the multicast group that are located in separate networks.

In one illustration, a root node of a network collects information fromnodes of its network to send to a central agent. In particular, the rootnode receives subscription messages regarding subscriptions of nodes ofits network to one or more multi cast groups. The root node may alsoreceive messages originating from nodes of adjacent networks.Additionally, or alternatively, the root node may receive messages fromnodes in its network indicating that the nodes can hear a node in anadjacent network. The root node compiles a list of multicast groups thathave members in its network and a list of networks that couldcommunicate with the network. These lists are sent to the central agent.In a similar fashion, other root nodes of other networks compile listsand send those lists to the central agent.

The central agent analyzes the lists from the root nodes to bridgecommunication for a multicast group. Specifically, the central agentdetermines networks that have members of the same multicast group. Forexample, the central agent may determine that a first network and asecond network both have members of the same multicast group. Thecentral agent also determines networks that are adjacent to each otherand/or are required to form a path to the networks that have members ofthe same multicast group. The central agent then sends a message to aroot node of a network requesting that communication between two or morenetworks be bridged for a multicast group.

Upon receiving the message from the central agent, the root node selectsa node to act as the bridge between the networks for the multicastgroup. The root node may select a node within its network that is ableto communicate with a node from the adjacent network for whichcommunication is being bridged. Various criteria for selecting the nodemay be used, such as minimum distance from a member of the multicastgroup, and so on. The root node sends a message down through the networkto the selected node instructing the selected node to bridgecommunication between the networks for the multicast group.

The bridging node then becomes a virtual member of the multicast group.In particular, the bridging node may send a subscription message for themulticast group to the root node of its network and a subscriptionmessage for the multicast group to the root node of the adjacentnetwork. Each subscription message indicates that the bridging node isbecoming a virtual member of the multicast group. This may cause a PSTto be formed within the two networks to facilitate distribution ofmulticast data for the multicast group. Thereafter, the bridging nodemay forward multicast data that originates in one network to members ofthe multicast group that are located in the adjacent network, and viceversa.

This process may be repeated any number of times for any number ofmulticast groups. For example, a node may be configured to act as abridge for a first multicast group and the same node or a different nodemay be configured to act as a bridge for a second multicast group. Assuch, connection points between networks may be created for variousmulticast groups.

In addition, this process may be repeated for any number of networks.For example, the central agent may determine that three or more networksneed to be bridged to facilitate distribution of multicast data for amulticast group. In some instances, each of the networks includes atleast one member of the multicast group. In other instances, a networkmay act as an intermediary connection between networks that includemembers of the multicast group. Here, the intermediary network may notinclude members of the multicast group, but may create a path ofdistribution between other networks.

The techniques are discussed in many instances in the context of ahierarchical tree-like network. For example, the techniques may beimplemented within a Routing Protocol for Low Power and Lossy Networks(RPL) where nodes are configured in a DODAG. However, the techniques maybe applied to other types of networks, such as a mesh network. Further,although the techniques are discussed in the context of multicastcommunication with any node of the network originating multicast datafor members of a multicast group (e.g., anysource multicast), thetechniques may be applied to other types of communication, such asunicast, and so on.

In some examples, the techniques may be implemented in the context of anadvanced metering infrastructure (AMI) of a utility communicationnetwork. However, the techniques described herein are not limited to usein a utility industry AMI. For example, the techniques may beimplemented in the context of Distribution Automation, Home EnergyManagement, or any other type of wireless or wired network. Unlessspecifically described to the contrary, the techniques described hereinare applicable to any communication network, control network, and/oranother type of network or system. In one example, the techniques may beimplemented in the context of the Internet of Things (IoT).

Example Environment

FIG. 1 is a diagram illustrating an example networked environment orarchitecture 100. The architecture 100 includes network communicationdevices 102(1)-102(N) (also referred to as nodes 102) associated with afirst Area Network (AN) and network communication devices 104(1)-104(M)(also referred to as nodes 104) associated with a second AN, where N andM are each an integer greater than or equal to 1. The networkcommunication devices 102 and/or the network communication devices 104may communicate with a service provider 106 via one or more networks 108(e.g., a backhaul network), such as the Internet. The node 102(1) maygenerally act as a root node to connect the nodes 102 of the first AN tothe service provider 106 via the one or more networks 108. Similarly,the node 104(1) may act as a root node to connect the nodes 104 of thesecond AN to the service provider 106 via the one or more networks 108.For instance, the nodes 102 may be configured in a Destination OrientedDirected Acyclic Graph (DODAG) with the node 102(1) acting as the DODAGroot, while the nodes 104 may also be configured in a DODAG with thenode 104(1) acting as the DODAG root. The node 102(1) and/or the node104(1) may comprise an edge device.

As used herein, the term “Area Network” (AN) refers to a defined groupof devices that are in communication with one another via one or morewired or wireless links. Examples of ANs include, for example, LocalArea Networks (LANs), Wide Area Networks (WANs), Neighborhood AreaNetworks (NANs), Personal Area Networks (PANs), Home Area Networks(HANs), Field Area Networks (FANs), and so on. In some instances,multiple ANs exist and collectively define a larger network, such as anadvanced metering infrastructure (AMI) of a utility communicationnetwork. In general, a network communication device is a member of aparticular AN. Although in some instances, a network communicationdevice may be a member of multiple ANs. Further, over time, networkcommunication devices may migrate from one AN to another geographicallyproximate or overlapping AN based on a variety of factors, such asrespective loads on the ANs, battery reserves, interference, or thelike.

The term “link” refers to a direct communication path between twodevices (without passing through or being relayed by another device). Alink may be over a wired or wireless communication path. Each link mayrepresent a plurality of channels over which a device is able totransmit or receive data. Each of the plurality of channels may bedefined by a frequency range which is the same or different for each ofthe plurality of channels. In some instances, the plurality of channelscomprises radio frequency (RF) channels. The plurality of channels mayinclude a data channel(s) and/or a control channel(s) that is designatedfor communicating messages to specify the data channel(s) to be utilizedto transfer data. Transmissions on a control channel may be shorterrelative to transmissions on a data channel. The AN may implement achannel hopping sequence, such that a channel may change over time.

The service provider 106 may provide remote resources to the networkcommunication devices 102 and/or 104. In some instances, the serviceprovider 106 comprise one or more central office systems that include asecurity service such as Authentication, Authorization and Accounting(AAA) server, a network registration service such as Dynamic HostConfiguration Protocol (DHCP) server, a network management service(NMS), a collection engine (CE), a meter data management system (in theutility context), a customer relationship management system (in thesales context), a diagnostic system (in a manufacturing context), aninventory system (in a warehouse context), a patient record system (inthe healthcare context), a billing system, etc. The networkcommunication devices 102 and/or 104 may register or interact with someor all of these one or more central office systems. In one example, theone or more central office systems may implement a meter data managementsystem to collect resource consumption data (e.g., data regarding usageof water, gas, electricity, etc. at a meter) from the networkcommunication devices 102 and/or 104, process the resource consumptiondata, provide data regarding resource consumption to customers,utilities, and others, and/or perform a variety of other functionality.In other instances, the service provider 106 comprises other systems toimplement other functionality, such as web services, cloud services, andso on. In yet other instances, the service provider 106 may beimplemented as other types of devices, such as in the context of theInternet of Things (IoT) that allows a variety of devices to exchangedata. In some instances, the service provider 106 may be referred to asa central agent.

The service provider 106 may be physically located in a single centrallocation, or may be distributed at multiple different locations. Theservice provider 106 may be hosted privately by an entity administeringall or part of the communications network (e.g., a utility company, agovernmental body, distributor, a retailer, manufacturer, etc.), or maybe hosted in a cloud environment, or a combination of privately hostedand cloud hosted services.

The service provider 106 may be implemented as one or more computingdevices including servers, desktop computers, or the like. In oneexample, the service provider 106 is configured in a server cluster,server farm, data center, mainframe, cloud computing environment, or acombination thereof. To illustrate, the service provider 106 may operateas a cloud computing device that provides cloud services, such asstorage, processing, and so on.

The network communication devices 102, the network communication devices104, and/or the service provider 106 may transmit and/or receiveProtocol Data Units (PDUs). A PDU may comprise a bit, frame, packet,segment, or another unit of data. A PDU may include control data and/orpayload data. As used herein, a message, transmission, communication, orthe like may refer to any type of PDU.

The network communication devices 102, the network communication devices104, and/or the service provider 106 may perform various operations tofacilitate the techniques discussed herein. For example, any of thenetwork communication devices 102 and/or 104 may form aPoint-to-Multipoint Sub-Tree (PST) for a multicast group and/ordistribute multicast data according to the PST. Additionally, oralternatively, the first AN of the nodes 102 may connect to the secondAN of the nodes 104, such as through a link 110.

Although the techniques are discussed in many instances with the ANsbeing implemented as tree-like structures having parent and child nodes,such as DODAGs, in some instances the ANs may be implemented indifferent network structures. For example, an AN may be implemented inwhole or part by other types of networks, such as hub-and-spokenetworks, mobile networks, cellular networks, etc. Regardless of thetopology of an AN, individual network communication devices maycommunicate by wireless (e.g., radio frequency) and/or wired (e.g.,power line communication, Ethernet, serial, etc.) connections.

Example Network Communication Device

FIG. 2 is a diagram showing details of an example node 200, such as anyof the network communication devices 102 and/or the networkcommunication devices 104 of FIG. 1. The node 200 may comprise any typeof network communication device (sometimes referred to as a node,computing device, or just device), such as a router (e.g., a field arearouter (FAR), a cellular router, an edge router, etc.), a utility meter(e.g., electricity, water, or gas meter), a relay (e.g., a cellularrelay), a repeater, a transformer, a sensor, a switch, a control device,an encoder/receiver/transmitters (ERTs), an appliance, a personalcomputer (e.g., a desktop computer, a laptop computer, etc.), a mobiledevice (e.g., a smartphone, a tablet, a personal digital assistant(PDA), an electronic reader device, etc.), a wearable computer (e.g., asmart watch, an optical head-mounted display (OHIVID), etc.), a server,an access point, a portable navigation device, a portable gaming device,a portable media player, a television, a set-top box, a computer systemsin an automobile (e.g., navigation system), a camera, a robot, ahologram system, a security system, a home-based computer system (e.g.,an intercom system, a home media system, etc.), a projector, anautomated teller machine (ATM), and so on. In some examples, the node200 is implemented as an edge device, such as a FAR, a cellular relay, acellular router, an edge router, a DODAG (Destination Oriented DirectedAcyclic Graph) root, a root device, and so on.

In some instances, the node 200 comprises a Limited Function Device(LFD), while in other instances the node 200 comprises a Full FunctionDevice (FFD). An FFD may include more functionality/resources than anLFD, such as different processing powers, processing capabilities, powerreliance, etc. In one example, an FFD is implemented as Mains PoweredDevice (MPD) that is connected to mains electricity (e.g., electricitymeters), while an LFD is implemented as a Battery Powered Device (BPD)that is not connected to mains electricity (e.g., a water meter, gasmeter, etc. that employs batteries). Since an MPD relies on mains power,the MPD may remain in an active state (e.g., a state associated withconsuming more than a threshold amount of power). Meanwhile, since a BPDrelies on battery power, the BPD may enter a sleep state (e.g., a stateassociated with consuming less than a threshold amount of power) whenthe BPD is not communicating or otherwise performing operations. The BPDmay use a communication schedule to determine when to enter a sleepstate and/or when to enter an active state. This may allow the BPD toconserve battery life.

While FFDs and LFDs may have the similar components, the components maydiffer due to the different constraints. As one example, while both anFFD and an LFD have transceivers, the specific transceivers used may bedifferent. For instance, a transceiver on an FFD may include a PLCmodem, while a transceiver on an LFD does not because it is notconnected to an electrical power line that could be used for PLCcommunications. Additionally, or alternatively, a transceiver on an LFDmay employ a lower power RF radio than and FFD to minimize energyconsumption. Further, other components of the FFDs and LFDs may vary. Insome instances, an LFD is implemented with less functionality and/orinclude less hardware components than an FFD. Further, in some instancescomponents of an LFD are lower power components than the correspondingcomponents of an FFD.

In one example of the architecture 100 of FIG. 1, the nodes 102(1) and104(1) each comprise an FFD, and the nodes 102(2)-102(N) and the nodes104(2)-(M) each comprise an LFD. In another example, the nodes 102(1)and 104(1) each comprise an LFD, and the nodes 102(2)-102(N) and thenodes 104(2)-(M) comprise one or more LFDs and/or FFDs.

As shown in FIG. 2, the example node 200 includes a processing unit 202,a transceiver 204 (e.g., radio, modem, etc.), one or more metrologydevices 206, a power supply unit 208, and a network interface 210. Theprocessing unit 202 may include one or more processors 212 and memory214. The one or more processors 212 may comprise microprocessors,central processing units, graphics processing units, or other processorsusable to execute program instructions to implement the functionalitydescribed herein. Additionally, or alternatively, in some examples, someor all of the functions described may be performed in hardware, such asan application specific integrated circuit (ASIC), a gate array, orother hardware-based logic device.

The transceiver 204 may comprise one or more hardware and/or softwareimplemented radios to provide two-way RF communication with othernetwork communication devices in an AN or another network. Thetransceiver 204 may additionally or alternatively include a modem toprovide power line communication (PLC) communication with other networkcommunication devices that are connected to an electrical service grid.

The metrology device(s) 206 may comprise the physical hardware andsensors to measure consumption data of a resource (e.g., electricity,water, or gas) at a site of the meter. In the case of an electric meter,for example, the metrology device(s) 206 may include one or more Halleffect sensors, shunts, or the like. In the case of water and gasmeters, the metrology device(s) 206 may comprise various flow meters,pressure sensors, or the like. The metrology device(s) 206 may reportthe consumption data to a service provider via the transceiver 204and/or the network interface 210. The consumption data may be formattedand/or packetized in a manner or protocol for transmission.

The power supply unit 208 may provide power to the node 200. In someinstances, such as when the node 200 is implemented as a FFD, the powersupply unit 208 comprises a mains power connector that couples to anAlternating Current (AC) or Direct Current (DC) mains power line wherethe node 200 is installed. In other instances, such as when the node 200is implemented as a LFD, the power supply unit 208 comprises a battery,such as a Lithium Thionyl Chloride battery (e.g., a 3 volt batteryhaving an internal impedance rated at 130 Ohms), a Lithium Manganesebattery (e.g., a 3 volt battery having an internal impedance rated at 15Ohms), a Lithium Ion battery, a lead-acid battery, an alkaline battery,and so on.

The memory 214 includes an operating system (OS) 216 and one or moreapplications 218 that are executable by the one or more processors 212.The memory 214 may also include one or more metrology drivers 220configured to receive, interpret, and/or otherwise process metrologydata collected by the metrology device(s) 206. Additionally, oralternatively, the one or more applications 218 may be configured toreceive and/or act on data collected by the metrology device(s) 206.

The memory 214 may also include one or more communication stacks 222. Insome examples, the communication stack(s) 222 may be configured toimplement a 6LowPAN protocol, an 802.15.4e (TDMA CSM/CA) protocol, an802.15.4-2015 protocol, and/or another protocol. However, in otherexamples, other protocols may be used, depending on the networks withwhich the node 200 is intended to be compatible. The communicationstack(s) 222 describe the functionality and rules governing how the node200 interacts with each of the specified types of networks. Forinstance, the communication stack(s) 222 may cause network communicationdevices to operate in ways that minimize the battery consumption of thenetwork communication devices when they are connected to these types ofnetworks.

The memory 214 may also store other information. For example, the memory214 may include a data structure that stores a member state indicatingwhether or not the node 200 is a member of a multicast group, aforwarding chain state indicating whether or not the node 200 ispositioned on a forwarding chain for a multicast group, a pruning stateindicating whether pruning is disabled or enabled for a multicast group,a child count of received subscriptions for a multicast group, aconscript state indicating whether or not the node 200 is acting as abridge, information about sub-nodes or child nodes (e.g., subscriptionsof child nodes to multicast groups, identifiers of multicast groups forsub-node or child nodes, any of the other information mentioned (but fora child node), etc.), identifiers of networks that have communicatedwith the network in which the node 200 is located, and so on.

In some instances, the node 200 may be configured to send or receivecommunications on multiple channels simultaneously. For example, thetransceiver(s) 204 may be configured to receive data at the same time onhundreds of channels. Additionally, or alternatively, the transceiver(s)204 may be configured to send data at the same time on hundreds ofchannels.

The various memories described herein (e.g., the memory 214) areexamples of computer-readable media. Computer-readable media may takethe form of volatile memory, such as random access memory (RAM) and/ornon-volatile memory, such as read only memory (ROM) or flash RAM.Computer-readable media devices include volatile and non-volatile,removable and non-removable media implemented in any method ortechnology for storage of information such as computer-readableinstructions, data structures, program modules, or other data forexecution by one or more processors of a computing device. Examples ofcomputer-readable media include, but are not limited to, phase changememory (PRAM), static random-access memory (SRAM), dynamic random-accessmemory (DRAM), other types of random access memory (RAM), read-onlymemory (ROM), electrically erasable programmable read-only memory(EEPROM), flash memory or other memory technology, compact diskread-only memory (CD-ROM), digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other non-transitorymedium that can be used to store information for access by a computingdevice. As defined herein, computer-readable media does not includetransitory media, such as modulated data signals and carrier waves,and/or signals.

While detailed examples of certain network communication devices (e.g.,the node 200) are described herein, it should be understood that thosenetwork communication devices may include other components and/or bearranged differently. As noted above, in some instances a networkcommunication device may include one or more processors and memorystoring processor executable instructions to implement thefunctionalities they are described as performing. Certain networkcommunication devices may additionally or alternatively include one ormore hardware components (e.g., application specific integratedcircuits, field programmable gate arrays, systems on a chip, and thelike) to implement some or all of the functionalities they are describedas performing.

By way of example and not limitation, the node 200 may implement avariety of modulation techniques and/or data rates, such asfrequency-shift keying (FSK) 802.15.4g (e.g., mandatory mode with a datarate of 50 kbps or 75 kbps, no forward error correction; legacy modewith a data rate of 150 kbps with forward error correction code rate1/2; option 2; etc.), offset quadrature phase-shift keying (OQPSK)modulation with direct-sequence spread spectrum (DSSS) spreading, and soon. To implement these different connection modes, a media accesscontrol (MAC) sub-layer of a device may be able to indicate to aphysical layer the modulation technique and data rate to be used foreach transmission.

Example Point-to-Multipoint Sub-Tree (PST)

FIGS. 3A-3B illustrate formation of an example Point-to-MultipointSub-Tree (PST) for a multicast group. In particular, FIG. 3A illustratesa network of nodes 302(A)-(S) before formation of the PST, while FIG. 3Billustrates the network of nodes 302(A)-(S) with indicators regardingthe PST. Here, the nodes 302(A)-(S) are configured in a Personal AreaNetwork (PAN), although the nodes 302(A)-(S) may form other types ofnetworks and/or be connected to other networks. Although many differentmulticast groups may be formed within a network, the example of FIGS.3A-3B illustrate the formation of the PST for a single multicast group(e.g., nodes join the same multicast group). In a similar fashion, PSTsmay be formed for other multicast groups. Further, in this example thenodes 302(A)-(S) are implemented in a Destination Oriented DirectedAcyclic Graph (DODAG) with the node 302(A) being a DODAG root.

In this example, in referencing FIG. 3A, the node 302(P) is the firstnode to join a multicast group. The node 302(P) updates data to indicatethat it is a member of the multicast group (e.g., sets its membershipstate to the multicast group to joined/enabled). The node 302(P) alsosends a subscription message (sometimes referred to as a “subscribemessage”) to its parent, the node 302(L). The subscription message maybe a Destination Advertisement Object (DAO) message or other message.The subscription message advertises that the node 302(P) is joining themulticast group. In many instances, the subscription message is sent asa unicast message. Although other forms of communication may be used,such as broadcast, multicast, etc.

The node 302(L) examines (e.g., views) the subscription message to seethat the node 302(P) is subscribing to the multicast group. The node302(L) updates its data to indicate the subscription of its child node,the node 302(P), to the multicast group. The node 302(L) also updatesits forwarding chain state to indicate that the node 302(L) is along aforwarding chain to the root node 302(A). The node 302(L) also updatesdata indicating a number of different child nodes from which the node302(L) has received a subscription message for the multicast group (alsoreferred to as child count of received subscriptions). The child countof received subscriptions accounts for the number of different childnodes, not the number of subscriptions messages received. The node302(L) then sends the subscription message on to its parent, the node302(I).

The node 302(I) examines (e.g., views) the subscription message to seethat the node 302(P) is subscribing to the multicast group. The node302(I) also updates its child count of received messages for themulticast group and updates its forwarding chain state to indicate thatthe node 302(I) is along a forwarding chain to the root node 302(A).

A forwarding chain state may indicate whether or not a node is on aforwarding chain. When enabled, the forwarding chain state indicatesthat the node is part of a forwarding chain. When disabled, theforwarding chain state indicates that the node is not part of aforwarding chain.

This process is repeated for each node from parent-to-parent until thesubscription message reaches the root node 302(A). In this example, thesubscription message travels from the node 302(P) to the node 302(L),from the node 302(L) to the node 302(I) from the node 302(I) to the node302(E), from the node 302(E) to the node 302(B), and from the node302(B) to the root node 302(A). This path may be referred to as aforwarding chain for the node 302(P). Thus, each of the nodes 302(L),302(I), 302(E), 302(B), and 302(A) has a forwarding chain state enabled.By sending the subscription message to the root node 302(A), the rootnode 302(A) may be aware of membership of its sub-nodes in multicastgroups. In many instances, the subscription message may maintain itsoriginal format (except header/footer data) on its way to the root node302(A). Although in other instances, the subscription message may bereformatted (e.g., data extracted and repackaged).

As noted above, as the subscription message traverses the network to theroot node 302(A), data at each node is updated. In particular, each ofthe nodes in the forwarding chain (the nodes 302(L), 302(I), 302(E),302(B), and 302(A)) will update its forwarding chain state to enabledfor the multicast group (e.g., indicating that the respective node isalong a forwarding chain for the multicast group). In addition, each ofthe nodes 302(L), 302(I), 302(E), 302(B), and 302(A) will update thechild count of received subscriptions to 1 in this example. Note thatthe child count of received subscriptions is zero for the node 302(P).In this example, it is assumed that no previous subscription messageshave been communicated before the communication of the subscriptionmessage for the node 302(P).

In addition to maintaining a forwarding chain state and a child count ofreceived subscriptions, each node maintains other data. For example,each node maintains a pruning state for each multicast group. A pruningstate may indicate whether or not to forward multicast data for amulticast group. The pruning state is initially enabled, meaning thatdata forwarding for the multicast group is not performed, generally. Inother words, in the default state of pruning enabled, data willgenerally not be forwarded from the node. As such, in the example ofFIG. 3A, the pruning state for each of the nodes 302 is initiallyenabled.

Although the nodes 302(B)-(S) do not generally maintain informationabout non-child nodes (e.g., the node 302(B) does not maintaininformation about a node two or more levels down, such as the node302(H)), the root node 302(A) maintains information about membership ofthe nodes of its network. In other words, the root node 302(A) maintainsdata indicating membership of the nodes 302(B)-(S) in one or moremulticast groups.

In continuing on in the example of FIGS. 3A-3B, the node 302(Q) nextsubscribes to the multicast group. The node 302(Q) changes itsmembership state for the multicast group to member and sends asubscription message to its parent, the node 302(L). The node 302(L)examines (e.g., views) the subscription message to see that the node302(Q) is subscribing to the multicast group and updates its data toindicate the subscription of the node 302(Q) to the multicast group. Thenode 302(L) then forwards the subscription message on to its parent, thenode 302(I), which updates its data. This process continues until thesubscription message reaches the root node 302(A). Again, as thesubscription message travels up the network, a forwarding chain isformed and data regarding a forwarding chain state and/or child count ofreceived subscriptions is updated. Here, the subscription messagetravels along the nodes 302(L), 302(I), 302(E), 302(B), and 302(A).

At this point, the node 302(L) has received a subscription message fromtwo child nodes, the node 302(P) and the node 302(Q). The node 302(L)has now become a common ancestor to the nodes 302(P) and 302(Q) (e.g.,child count of subscription is greater than 1), since the node 302(L)joins two or more branches. When this occurs, the node 302(L) sends amessage (e.g., MinP) to each of the child nodes 302(P) and 302(Q)instructing the respective node to disable the pruning state. In otherwords, the message instructs the respective node to change to a state inwhich data is forwarded from the respective node. The MinP message maybe a DODAG Information Object (DIO) or another message. Upon receipt ofthe respective message, the node 302(P) and the node 302(Q) change thepruning state to disabled. This will allow multicast data thatoriginates at, for example, the node 302(P) to be sent up to the node302(L) and back down to the node 302(Q) (e.g., from one branch toanother), or vice versa.

Next, the node 302(L) joins the multicast group. The node 302(L) changesits membership state for the multicast group to member and sends asubscription message to its parent, the node 302(I). The subscriptionmessage is sent node-by-node up the network until it reaches the rootnode 302(A). Again, as the subscription message travels up the network,a forwarding chain is formed and data regarding a forwarding chain stateand/or child count of received subscriptions is updated. Here, thesubscription message travels the nodes 302(I), 302(E), 302(B), and302(A). At this point, the node 302(L) has enabled the forwarding chainstate and the member state for the multicast group. Also, note that thenode 302(I) has received multiple subscription messages, but all ofthose subscription messages have come from the node 302(L). Thus, thechild count of received subscriptions for the node 302(I) is still 1.Each of the nodes 302(E), 302(B), and 302(A) also has a child count ofreceived subscriptions of 1.

Next, the node 302(R) joins the multicast group. The node 302(R) changesits membership state for the multicast group to member and sends asubscription message to its parent, the node 302(M). The subscriptionmessage is sent node-by-node up the network until it reaches the rootnode 302(A). Again, as the subscription message travels up the network,a forwarding chain is formed and data regarding a forwarding chain stateand/or child count of received subscriptions is updated. Here, thesubscription message travels the nodes 302(M), 302(I), 302(E), 302(B),and 302(A).

Since the child count of received subscriptions for the node 302(I) hasnow changed to 2 (e.g., the node 302(I) is a common ancestor), the node302(I) sends a message (e.g., MinP) to each of the child nodes 302(L)and 302(M) instructing the respective node to disable the pruning state.In addition, once the message to disable the pruning state is receivedat the node 302(M), the node 302(M) sends a message (e.g., MinP) to itschild, the node 302(R), to disable its pruning state. Since the pruningstates are already disabled in the child nodes for the node 302(L)(e.g., the nodes 302(P) and 302(Q)), the node 302(L) does not need tosend a message to its child nodes to disable the pruning state.

In this example, the node 302(K) joins the multicast group next. Thenode 302(K) changes its membership state for the multicast group tomember and sends a subscription message to its parent, the node 302(H).The subscription message is sent node-by-node up the network until itreaches the root node 302(A). Again, as the subscription message travelsup the network, a forwarding chain is formed and data regarding aforwarding chain state and/or child count of received subscriptions isupdated. Here, the subscription message travels the nodes 302(H),302(D), 302(B), and 302(A).

The child count of received subscriptions for the node 302(B) has nowchanged to 2 and the node 302(B) is now a common ancestor. Inparticular, the node 302(B) has received at least one subscriptionmessage from the node 302(E) and also at least one subscription messagefrom the node 302(D).

A subscription message does not need to indicate a subscription for adirect child node to count towards the child count of receivedsubscriptions. For example, the subscription message for the node 302(K)to join the multicast group, which is sent up to the node 302(B) throughintermediary nodes, counts toward the child count of receivedsubscriptions for the node 302(B), even though the subscription messageis for a node that it several levels down. In addition, the varioussubscription messages received by the node 302(B) from the node 302(E)for nodes within that sub-tree, cause the child count of receivedsubscriptions for the node 302(B) to be incremented by just one, sincethe subscription messages were all received from the same child, thenode 302(E). As such, the child count of received subscriptions accountsfor the number of different child nodes, not the number of subscriptionsmessages received.

When the node 302(B) becomes a common ancestor, the node 302(B) sends amessage (e.g., MinP) to each of the child nodes 302(D) and 302(E)instructing the respective node to disable the pruning state. Themessage may be sent as either a unicast to each child node or amulticast to all neighboring nodes of the node 302(B). In manyinstances, such message will only be processed if it is received fromthe node's PST parent (e.g., the node to which it sends its subscribemessages).

Upon receiving the message, the node 302(D) sends a message (e.g., MinP)to its child, the node 302(H) to disable the pruning state. Then, uponreceipt of such message at the node 302(H), the node 302(H) sends amessage (e.g., MinP) to its child, the node 302(K), to disable thepruning state. The node 302(D) does not need to send such a message tothe child node 302(G), since it knows that the child node 302(G) is nota member of the multicast group or part of a forwarding chain.Similarly, in the other branch, upon receipt of the message at the node302(E), the node 302(E) sends a message (e.g., MinP) to its child, thenode 302(I), to disable the pruning state. The child nodes to the node302(I) have already disabled the pruning state and so a message todisable the pruning state is not further distributed along thatsub-tree. By disabling the pruning states of the nodes 302(K), 302(H),302(D), 302(E), and 302(I), the techniques may allow multicast data inone branch to reach the other branch.

Here, the nodes 302(M) and 302(I) similarly join the multicast group bychanging a membership state for the multicast group to member andsending a subscription message up the network to the root node 302(A). Aforwarding chain for each of the nodes 302(M) and 302(I) is formed asthe respective subscription message is forwarded up to the root node302(A).

FIG. 3B illustrates the example PST that has been formed. As illustratedwith light stippling, the nodes 302(K), 302(P), 302(Q), and 302(R) aremembers of the multicast group. As illustrated with dense stippling, thenodes 302(I), 302(L), and 302(M) are both members of the multicast groupand have the forwarding chain state enabled. Thus, a group 304 includesthe members of the multicast group. As illustrated with dashed lines,the nodes 302(B), 302(D), 302(E), and 302(H) have the forwarding chainstate enabled for the PST. Thus, a group 306 includes nodes that act asrelays for multicast data (e.g., they relay or forward multicast data).Although not shown in this example, in some instances the root node302(A) also has a forwarding chain state enabled.

In FIG. 3B, each of the nodes 302(A)-(S) shows a child count of receivedsubscriptions in the middle of the respective node. Further, the nodeswith the pruning state disabled are shown with a darker outline (i.e.,the nodes 302(D), 302(E), 302(H), 302(I), 302(K), 302(L), 302(M),302(P), 302(Q), and 302(R)).

This PST may allow data to be forwarded along paths that lead to membersof the multicast group. Multicast data may generally be forwarded from anode (either upwards or downwards in the network) if at least one of thefollowing conditions is satisfied: (i) the node is set to a state inwhich data is forwarded from the node for the multicast group (e.g., thepruning state is disabled), or (ii) the node has received a subscriptionmessage for the multicast group from two or more different child nodes(e.g., the child count of received subscriptions is two or greater—thenode is a common ancestor).

In the example of FIGS. 3A-3B, any member of the multicast group mayinitiate multicast data for members of the multicast group. That is, themulticast group comprises an anycast group where each member of themulticast group is configured to initiate a multicast communication.

To illustrate distribution of data in the example of FIG. 3B, assumethat the node 302(R) desires to send data to all members of themulticast group. The node 302(R) will transmit the data. The data can bereceived by all neighboring nodes. Here, the data is received by thenode 302(M). The node 302(M) will then transmit the data, since itspruning state is disabled. The node 302(I) will hear and receive thetransmission. The node 302(I) will then transmit the data, since itspruning state is disabled. The nodes 302(E) and 302(L) will each hearand receive the transmission. The node 302(L) will transmit the data(since its pruning state is disabled), which is heard and received bythe nodes 302(P) and 302(Q). Further, the node 302(E) will transmit thedata upon receiving the transmission from the node 302(I) The node302(E) will transmit the data since its pruning state is disabled. Thetransmission may be heard and received by the node 302(B). The node302(B) will transmit the data, since the node 302(B) has a child countof received subscriptions of 2. This will occur even though the pruningstate for the node 302(B) is enabled. The transmission is heard andreceived by the node 302(D). The node 302(D) then transmits the data,which is heard and received by the node 302(H). The node 302(H) maytransmit the data (since its pruning state is disabled), which is heardand received by the node 302(K). As such, data is forwarded if the nodehas the forwarding chain state enabled and the pruning disabled, or ifthe node is a common ancestor (e.g., child count of receivedsubscriptions is greater than 1). In this illustration, data is limitedto being distributed within a particular sub-tree of the network (e.g.,a sub-tree rooted at the node 302(B)).

In this illustration, the node 302(A) may receive the multicast datafrom the node 302(B) (e.g., if the data is transmitted as a multicasttransmission). However, the node 302(A) will not forward on themulticast data, since the pruning state is disabled and the child countof received subscriptions is 1. This limits the multicast data frombeing distributed down into the branch of the node 302(C). Further, thenode 302(G) may hear the multicast data transmitted by node 302(D), butthis data may be disregarded by the node 302(G), since it is neither amember of the multicast group nor forwarding for this multicast group.Similarly, the multicast data may be heard by the node 302(O) where itwould be disregarded.

Although not illustrated in FIGS. 3A-3B, a message (e.g., MinP) todisable a pruning state may be sent in other instances than thosedescribed above. In one example, a node that is a member-in-path (alsoreferred to as a member ancestor) may send a message to a child node todisable a pruning state. In returning to the state described above inFIG. 3A when there only two members of the multicast group (the node302(P) and the node 302(Q)), let's assume that the node 302(E) becomesthe next member of the multicast group. Here, the node 302(E) determinesthat is it part of a forwarding chain for a member of the multicastgroup (e.g., it is along a forwarding chain for the node 302(P) and thenode 302(Q)). Further, the node 302(E) is now a member. As such, thenode 302(E) is a member ancestor to the member nodes 302(P) and 302(Q).In other words, the node 302(E) is a member along a path to the rootnode 302(A). The node 302(E) should now be included in multicastcommunications. As such, the node 302(E) sends a message to its child,the node 302(I), instructing the node 302(I) to disable the pruningstate. This causes the node 302(I) to send a message to its child, thenode 302(L), to disable the pruning state. Such message is not sent tothe node 302(M), since it is not part of a forwarding chain. Thus,pruning states are disabled along the forwarding chains. In thisillustration, by disabling the pruning states of the node 302(I) and302(L), multicast data may be distributed among the members of themulticast group (the nodes 302(P), 302(Q), and 302(E)) via the nodes302(L) and 302(I).

Furthermore, although the example of FIGS. 3A-3B show the formation of aPST with particular nodes, the PST may be formed with any number ofnodes and/or dynamically updated over time. For example, as nodessubscribe or unsubscribe to the multicast group, the PST may be updatedso that data forwarding is limited in a different manner.

Example Network Bridging

FIGS. 4A-4B illustrate an example of bridging communication betweennetworks to facilitate distribution of multicast data. FIGS. 4A-4Billustrate a network 400 having nodes 402(A)-402(R) (collectivelyreferred to as “nodes 402”) and a network 404 having nodes 406(A)-406(T)(collectively referred to as “nodes 406”). In particular, FIG. 4Aillustrates the networks 400 and 404 before a communication bridge hasbeen established, while FIG. 4B illustrates the networks 400 and 404after establishing the communication bridge. Here, the networks 400 and404 are Personal Area Networks (PANs), although the networks 400 and 404may be other types of networks. Further, in this example, the networks400 implements a DODAG with the node 402(A) being a DODAG root, and thenetwork 404 implements a DODAG with the node 406(A) being a DODAG root.

In reference to FIG. 4A, as the nodes 402 join the network 400, thenodes 402 may send messages up the network 400 to the root node 402(A)indicating such subscription to the network 400. In some instances, themessages are DAO messages, while in other instances the messages areother types of messages. If a node is able to communicate with a node ofanother network, a message may be sent from the node up through theother network to the root node of the other network. In the example ofFIGS. 4A-4B, the node 402(R) joins the network 400. Further, the node402(R) is able to communicate with the node 406(T) (e.g., the node406(T) could have been selected as a parent). Here, the node 402(R) maysend a message (also referred to as a membership message) to the node406(T) indicating that the node 402(R) has become a member of thenetwork 400 (e.g., a message with a source address identifying thenetwork 400). The message may traverse the network 404 to the root node406(A).

In a similar fashion, as the nodes 406 join the network 404, the nodes406 may send messages up the network 404 to the root node 406(A)indicating such membership to the network 404. In some instances, themessages are DAO messages, while in other instances the messages areother types of messages. As noted above, in this example the nodes402(R) and 406(T) are able to communicate with each other. Thus, thenode 406(T) also sends a message to the node 402(R) indicatingmembership of the node 406(T) to the network 404. This message traversesthe network 400 up to the root node 402(A).

In this example, the node 402(R) may send a membership message up to thenode 406(A) of the adjacent network 404, and/or the node 406(T) may senda membership message up to the node 402(A) of the adjacent network 400.In other examples, a node may send a message to a root node of itsnetwork indicating that it is able to communicate with a node of anadjacent network. For example, the node 402(R) may generate a messageand send such message up to its root node 402(A) indicating that it isable to communicate with a node of the network 404.

Further, as the nodes 402(J), 402(I), 402(K), 402(L), 402(N), 402(O),and 402(P) become members of a multicast group, the nodes 402(J),402(I), 402(K), 402(L), 402(N), 402(O), and 402(P) may send membershipmessages through the network 400 node-by-node to the root node 402(A).In some instances, the membership messages are DAO messages, while inother instances the membership messages are other types of messages.Likewise, as the nodes 406(I), 406(L), 406(M), 406(P), 406(Q), and406(R) become members of the same multicast group, the nodes 406(I),406(L), 406(M), 406(P), 406(Q), and 406(R) may send subscriptionmessages through the network 404 node-by-node to the root node 406(A).

Based on receipt of various messages, the root node 402(A) may maintaina list of networks that have communicated with the network 400 and/or alist of multicast groups associated with the network 400. In thisexample, the list of networks that have communicated with the network400 may include the network 404 (e.g., a network identifier for thenetwork 404). Further, the list of multicast groups may include themulticast group that the nodes 402(J), 402(I), 402(K), 402(L), 402(N),402(O), and 402(P) are members of (e.g., a multicast identifier oraddress for the multicast group). The root node 402(A) may send the listof networks and/or the list of multicast groups to a central agent, suchas the service provider 106 of FIG. 1.

Meanwhile, based on receipt of various messages, the root node 406(A)may maintain a list of networks that have communicated with the network404 and/or a list of multicast groups associated with the network 404.In this example, the list of networks that have communicated with thenetwork 404 may include the network 400. Further, the list of multicastgroups may include the same multicast group that its sub-nodes aremembers of. The root node 406(A) may send the list of networks and/orthe list of multicast groups to the central agent.

The central agent may process the information received from the rootnode 402(A) and the information from the root node 406(A) to determine aplurality of networks that are needed to bridge communication for themulticast group. Each network of the plurality of networks may beadjacent to at least one other network of the plurality of networks. Inother words, the plurality of networks may be a chain of adjacentnetworks that are needed to distribute data to members of the multicastgroup. In this example, the central agent determines that the networks400 and 404 need to be bridged for the multicast group.

The central agent may then determine a bridge list for one or morenetworks, such as each network or a particular number of networks. Thebridge list may indicate adjacent networks of the plurality of networksthat a particular network needs to connect to in order to facilitatedistribution of multicast data. In this example, the central agentdetermines a bridge list for the network 400. This bridge list includesthe network 404 (e.g., a network identifier for the network 404).

Although the central agent may instruct either or both of the networks400 and 404 to bridge communication for the multicast group, in thisexample the central agent instructs the network 400, since the root node402(A) received a message indicating that a node from its network isable to communicate with a node from the network 404. In particular, thecentral agent sends a message to the root node 402(A) with the bridgelist for the multicast group to bridge to the network 400. In otherwords, the central agent requests that the network 400 bridgecommunication to the network 404 for the multicast group.

Upon receipt of such message, the root node 402(A) may select a node toact as the bridge between the networks 400 and 404. The root node 402(A)may generally select a node that has communicated with a node from thenetwork 404 in the past. In this example, the root node 402(A) selectsthe node 402(R) to act as the bridge (also referred to as a“conscript”). The root node 402(A) may send a message through thenetwork 400 to the node 402(R) requesting that the node 402(R) bridgecommunication to the network 404. In some instances, the message is sentin a DIO communication, while in other instances the message is sent inother formats.

The node 402(R) is then configured to bridge communication between thenetworks 400 and 404, as illustrated in FIG. 4B. In this example, thisincludes configuring the node 402(R) to act as a virtual member of themulticast group. In general, a virtual member of a multicast groupperforms operations like a member of the multicast group, but withoutprocessing multicast data for the multicast group, as discussed infurther detail below. To become a virtual member, the node 402(R) maysend a subscription message up the network 400 to the root node 402(A)indicating that the node 402(R) is joining the multicast group as avirtual member. The node 402(R) may also send, via a link 408, asubscription message to the node 406(T) of the network 404 indicatingthat the node 402(R) is joining the multicast group as a virtual member.This subscription message may traverse the network 404 to reach the rootnode 406(A).

As the subscription message is sent up the network 400 and up thenetwork 404, a portion of a PST may be formed for the multicast group.For example, the node 406(B) may become a common ancestor after thesubscription message is sent up to the root node 406(A). This causes thenode 406(B) to send a message to the child nodes 406(D) and 406(E) todisable a pruning state. The message to disable a pruning state maypropagate down the nodes from the node 406(D) to the node 406(R) todisable a pruning state in each of these nodes. Further, after sendingthe subscription message up to the root node 402(A), the node 402(R) nowhas a member in its path to the root node 402(A) (e.g., a member alongthe forwarding chain). This cause the node 402(P) to send a message tothe node 402(Q) to disable a pruning state.

As illustrated in FIG. 4B, a group of nodes 410 may be relays for themulticast group. In other words, these nodes may assist in distributingmulticast data for the multicast group to all members of the multicastgroup in both the network 400 and the network 404. The node 402(R) mayact as the bridge between the network 400 and the network 404.

Although the example of FIGS. 4A-4B discusses the root node 402(A)communicating with the node 402(R) to become the bridge, in someinstances the network 404 may facilitate such processing. For example,the root node 406(A) may send a message to the node 406(T) instructingthe node 406(T) to communicate with the node 402(R) to cause the node402(R) to become the bridge.

Example Processes

FIGS. 5 and 6A-6B illustrate example processes 500 and 600 for employingthe techniques discussed herein. For ease of illustration the processes500 and 600 may be described as being performed by various devicesdiscussed herein. However, the processes 500 and 600 may be performed byany type of device, such as the service provider 106, the node 200, orany other device.

The processes 500 and 600 (as well as each process described herein) areillustrated as logical flow graphs, each operation of which represents asequence of operations that can be implemented in hardware, software, ora combination thereof. In the context of software, the operationsrepresent computer-readable instructions stored on one or morecomputer-readable storage media that, when executed by one or moreprocessors, perform the recited operations. Generally, computer-readableinstructions include routines, programs, objects, components, datastructures, and the like that perform particular functions or implementparticular abstract data types. In some contexts of hardware, theoperations may be implemented (e.g., performed) in whole or in part byhardware logic components. For example, and without limitation,illustrative types of hardware logic components that can be used includeField-programmable Gate Arrays (FPGAs), Application-specific IntegratedCircuits (ASICs), Application-specific Standard Products (ASSPs),System-on-a-chip systems (SOCs), Complex Programmable Logic Devices(CPLDs), etc. The order in which the operations are described is notintended to be construed as a limitation, and any number of thedescribed operations can be combined in any order and/or in parallel toimplement the process. Further, any number of the described operationsmay be omitted.

FIG. 5 illustrates the example process 500 to form a Point-to-MultipointSub-Tree (PST) and/or distribute data according to the PST.

At 502, the node 200 may form at least a portion of the PST. This mayinclude performing a variety of operations. In one example, the node 200receives, from a child node, a subscription message advertisingmembership to the multicast group. The subscription message may indicatethat the child node is subscribing to the multicast group and/or that anode along a branch including the child node is subscribing to themulticast group. The node 200 may view the subscription message andupdate a data structure. The data structure may maintain a child countof received subscriptions, subscription information for the node 200(e.g., what multicast groups the node 200 is a member of), subscriptioninformation for other nodes (e.g., what multicast groups the sub-nodesto the node 200 are members of), a pruning state of the node 200 (e.g.,enabled or disabled), a forwarding chain state of the node 200 (e.g.,enabled or disabled), and so on. The node 200 may forward thesubscription message up the network to a parent node (e.g., a node thatis fewer hops to a root node than the node 200), so that thesubscription message may reach a root node. This may form a forwardingchain for the node that originated the subscription message. In anotherexample, the node 200 may generate a subscription message itself andsend that message up the network to a parent node.

In yet another example, the node 200 may form a portion of the PST bysending a message to a child node to change a pruning state of the childnode. In one illustration, the node 200 may send a message (e.g., MinP)to change a pruning state when the node 200 becomes a common ancestor.Here, the node 200 may have received a subscription message from a firstchild node advertising membership to the multicast group and asubscription message from a second child node advertising membership tothe multicast group. The node 200 may update the child count of receivedsubscriptions to 2 and determine that the node has received asubscription message for the multicast group from two or more differentchild nodes (e.g., the child count of received subscriptions is morethan a threshold). Based on such determination, the node 200 may send amessage to the first child node and/or the second child node instructingthe respective child node to disable a pruning state to allow dataforwarding from the child node for the multicast group. In anotherillustration, the node 200 may send a message to change a pruning statewhen the node 200 is a member-in-path for the multicast group. Here, thenode 200 may determine that it has transitioned to being a member of themulticast group and that the node 200 is part of a forwarding chain fora member of the multicast group. Alternatively, or additionally, thenode 200 may determine that it is a member of the multicast group andthat a sub-node has transitioned to being a member of the multicastgroup (e.g., the node 200 is now a member-in-path). Based on eitherdetermination, the node 200 may send a message to a child node todisable a pruning state. The message may traverse downward along aforwarding chain to allow data forwarding for the multicast group fornodes along the forwarding chain.

At 504, the node 200 may refresh membership information and/or a pruningstates. The operation 504 may be performed to deal with network topologychanges (e.g., nodes joining or leaving the network). For example,periodic subscription messages may be sent by the node 200 to a parentnode (e.g., its best parent) to announce its membership to a multicastgroup. Additionally, or alternatively, the node 200 may periodicallysend a message to a child node to disable or enable a pruning state ofthe child node.

At 506, the node 200 may receive data destined for members of amulticast group. The data may be received from a child node, a parentnode, or any other neighboring node (e.g., direct neighbor).

At 508, the node 200 may determine a pruning state of the node 200and/or a child count of received subscriptions. For example, the node200 may determine if the pruning state is enabled for the multicastgroup or if the pruning state is disabled. Additionally, oralternatively, the node 200 may determine a number of different childnodes from which the node 200 has received a subscription to themulticast group (e.g., the child count of received subscriptions).

At 510, the node 200 may determine whether or not to forward the data toan adjacent node. That is, the node 200 may determine whether or not itneeds to forward the data to propagate the data to one or more membersof the multicast group. For example, the node 200 may determine toforward the data when the pruning state is disabled for the node 200and/or the node 200 has received at least a subscription message for themulticast group from a first child node and a subscription message forthe multicast group from a second child node (e.g., the child count ofreceived subscriptions is greater than 1). Alternatively, the node 200may determine to not forward the data when the pruning state is enabledfor the node 200 and the node 200 has not received at least asubscription message for the multicast group from a first child node anda subscription message for the multicast group from a second child node(e.g., the child count of received subscriptions is less than 2).

If the node 200 determines to forward the data to the adjacent node, theprocess 500 may proceed to operation 512 (e.g., the YES branch). If thenode determines to not forward the data to the adjacent node, theprocess 500 may proceed to operation 514 (e.g., the NO branch).

At 512, the node 200 may forward the data to the adjacent node. Thisincludes transmitting the data, which may be heard and/or received byany neighboring nodes (e.g., an adjacent node). The adjacent node may bea neighboring node that is a child, parent, or another node. Theadjacent node may be a member of the multicast group. Alternatively, theadjacent node may not be a member of the multicast group.

At 514, the node 200 may refrain from forwarding the data to theadjacent node.

FIGS. 6A-6B illustrate the example process 600 to bridge communicationbetween multiple networks to facilitate distribution of multicast data.For ease of discussion, the process 600 is illustrated as beingperformed by various devices, such as a service provider 602 (like theservice provider 106 of FIG. 1), a root node 604 of a second network, aroot node 606 of a first network, a bridge node 608 of the firstnetwork, and a node 610 of the second network. In many instances, theservice provider 602 implements a central agent to bridge communicationbetween networks.

In FIGS. 6A-6B, a first network of node(s) 612 is illustrated betweenthe root node 606 and the bridge node 608. This represents one or morenodes of the first network. For example, communications between the rootnode 606 and the bridge node 608 may generally occur via the firstnetwork of node(s) 612 (e.g., node-by-node through the first network).However, in other instances the first network of node(s) 612 iseliminated and the root node 606 and the bridge node 608 communicatedirectly with each other.

In FIG. 6A, at 614, the bridge node 608 and the node 610 maycommunicate. This may include sending and/or receiving any number ofcommunications to discover each other. For example, the bridge node 608and/or the node 610 may send a message (e.g., broadcast) to neighboringnodes to discover other proximate nodes and/or form a parent-childrelationship. Based on such communication, the bridge node 608 and/orthe node 610 may join a network (e.g., form a parent-child relationshipwith a node of a network). During this process, the bridge node 608 andthe node 610 discover that they are within communication range of eachother, but ultimately the bridge node 608 joins the first network andthe node 610 joins the second network.

At 616(A), the node 610 may send a message to the bridge node 608, andat 616(B), the bridge node 608 may forward that message on to the rootnode 606. The message may indicate membership of the node 610 to thesecond network. The message may include a network identifier (e.g., PANidentifier) of the second network. In some instances, the message issent in a DAO communication, while in other instances the message issent in other types of communications. As such, the message may indicatethat the node 610 has communicated with the bridge node 606 and/or thatthe bridge node 608 could potentially be a parent to the node 610. Bysending such message into a neighboring network (i.e., the secondnetwork), the root node 606 of the neighboring network may identifyadjacent networks.

Although not illustrated in FIG. 6A, the node 610 may also send amessage to the root node 604 of its own network, the second network. Themessage may indicate membership of the node 610 to the second network.

Further, although also not illustrated in FIG. 6A, the bridge node 608may similarly send a message up to the root node 606 of the firstnetwork and a message up to the root node 604 of the second network.Each message may indicate membership of the bridge node 608 to the firstnetwork.

At 618, the root node 606 may receive the message originating from thenode 610. The root node 606 may also receive one or more subscriptionmessages from the first network node(s) 612 (or the bridge node 608)indicating subscription of the first network node(s) 612 (or the bridgenode 608) to one or more multicast groups. The root node 606 may receivesubscription messages over time as nodes subscribe to one or moremulticast groups.

At 620, the root node 606 may build a list of networks that havecommunicated with the first network and/or a list of multicast groupsthat have members in the first network. For example, upon receiving themessage originating from the node 610 and identifying the secondnetwork, the root node 606 may update the list of networks to indicatethat a node of the first network has received a communication from anode of the second network. Here, a network identifier for the secondnetwork may be included in the list of networks. In another example,upon receiving a subscription message indicating that a particular nodeis subscribing to a multicast group, the root node 606 may update thelist of multicast groups for the first network to indicate that theparticular node is a member of the multicast group. Here, a multicastgroup identifier (e.g., multicast group address) may be included in thelist of multicast groups. As such, as part of operation 620, the rootnode 606 may determine that a node of the first network has communicatedwith a node of the second network and/or that the first network includesa member of a particular multicast group.

At 622, the root node 606 may send information to the service provider602. The information may include the list of networks and/or the list ofmulticast groups.

At 624, the service provider 602 may receive the information from theroot node 606.

At 626, the root node 604 of the second network may send information tothe service provider 602, and at 628, the service provider 602 mayreceive the information. The information may include a list of networksthat have communicated with the second network and/or a list ofmulticast groups that have members in the second network. Suchinformation may have been created at the root node 604 in a similarfashion as that done at operation 620 (e.g., as messages are receivedindicating subscriptions and/or communication with other networks).

At 630, the service provider 602 may process the information receivedfrom the root node 604 and the information received from the root node606. For example, the service provider 602 may analyze the lists ofmulticast groups received from the root nodes 604 and 606 to build, foreach multicast group, a list of networks that include at least onemember of the respective multicast group. The service provider 602 mayalso analyze the lists of networks received from the root nodes 604 and606 to determine a plurality of networks that are needed to bridgecommunication to a list of networks that include at least one member fora particular multicast group. Each network of the plurality of networksmay be adjacent to at least one other network of the plurality ofnetworks. In other words, the plurality of networks may be a chain ofadjacent networks that are needed to distribute data to members of theparticular multicast group. The service provider 602 may then determinea bridge list for a particular network. The bridge list may indicateadjacent networks of the plurality of networks that the particularnetwork needs to connect to in order to facilitate distribution ofmulticast data. This process may be repeated for each multicast group.

In one illustration, assume network A has a member in a multicast groupand is adjacent to network B that also has a member in the samemulticast group. The bridge list for the network A for the multicastgroup would include the network B, and the bridge list for the network Bfor the multicast group would include the network A.

In another illustration, assume that network Q is adjacent to network R,and network R is adjacent to network S. Also, assume that only networksQ and S include members in the same multicast group. Here, the network Qwould need to bridge to the network R, and the network R would need tobridge to the network S in order to form a path of distribution. Thus,the networks Q, R, and S are needed to bridge communication. As such,the bridge list for the network Q would include the network R, eventhough the network R does not include a member of the multicast group.Further, the bridge list for the network R would include the networks Qand S, and the bridge list for the network S would include the networkR.

Although the operation 630 is discussed in the context of creating abridge list for each network of a plurality of networks that are neededto bridge communication for a multicast group, in some instances alimited number of bridge lists are created, such as those needed to formsufficient bridges to connect the plurality of networks. For example, inreturning to the illustration above with the networks Q, R, and S, thebridge list for the network R may be the only bridge list that iscreated, since the network R is able to connect to both the networks Qand S (e.g., it's an intermediary network).

At 632, the service provider 602 may determine to bridge communicationbetween multiple networks for a multicast group to allow distribution ofmulticast data to members of the multicast group. The determination maybe based on the processing at operation 630. For example, the serviceprovider 602 may determine to bridge the first network and the secondnetwork for a multicast group when the first network and the secondnetwork each have at least one member to the multicast group. In someinstances, the service provider 602 may determine to bridgecommunication for adjacent networks that include members in the samemulticast group. In other instances, the service provider 602 maydetermine to bridge communication for networks that include members inthe same multicast group, but are not adjacent networks. Here, theservice provider 602 may determine to use an intermediary networkwithout members in a multicast group.

At 634, the service provider 602 may send a message to the root node 604and/or the root node 606. The message may request that communication bebridged with another network for a multicast group to allow distributionof multicast data to members of the multicast group. The message mayinclude a bridge list for a multicast group. Although operation 634 isillustrated as sending a message to the root node 604 and the root node606, in many instances the message is sent to only one of the rootnodes. This may avoid duplicative processing at the root nodes toconfigure a node to bridge communication and/or reduce duplicatemulticast data at some nodes.

In the example illustrated in FIG. 6A, the first network and the secondnetwork are adjacent to each other and each include at least one memberin the same multicast group. Here, the service provider 602 sends amessage to either the root node 604 and/or the root node 606 requestingthat communication be bridged between the first and second networks forthe multicast group. The service provider 602 may send a bridge list tothe root node 604 and/or the root node 606. For instance, if the messageis sent to the root node 606, the bridge list for the multicast groupfor the root node 606 would list the second network (e.g., list thenetwork identifier for the second network).

In another example, not illustrated in FIG. 6A, assume that the firstnetwork and the second network are not adjacent to each other, but athird network is positioned between the two. Also, assume that the firstnetwork and the second network include members in the same multicastgroup, but the third network does not. Here, the service provider 602may send a message to any of the root nodes requesting thatcommunication be bridged for the multicast group. For instance, themessage may be sent to the root node of the third, intermediary networkwith the bridge list for the multicast group. The bridge list may listthe first network and the second network.

At 636, the root node 604 may receive the message from the serviceprovider 602 regarding a communication bridge between networks for amulticast group.

Alternatively, or additionally, at 638, the root node 606 may receivethe message from the service provider 602 regarding a communicationbridge.

The example of FIGS. 6A-6B focuses on the root node 606 receiving themessage and performing processing based on such receipt, as discussedbelow. Although similar processing may be performed by the root node604.

Upon receiving the message regarding the communication bridge at 638,the root node 606 may check to see (i) if the root node 606 has receiveda subscription message (to the multicast group) that originated at anode of the second network (e.g., is the node 610 a member of themulticast group), or (ii) if a node of the first network that hascommunicated with a node of the second network is a member of themulticast group (e.g., is the node 608 a member of the multicast group).In other words, the root node 606 checks to see if a node of the second,adjacent network that is able to communicate with the first network is amember of the multicast group and/or a node of the first network that isable to communicate with the second network is a member of the multicastgroup.

If the condition (i) and/or the condition (ii) is true (e.g., either orboth of those nodes is a member), then the root node 606 does not needto do anything. Here, a PST would have already been established to linkcommunication for the multicast group between the two networks. In otherwords, no bridge node is needed, because the networks would already beconfigured to distribute multicast data between the networks for themulticast group. For example, if the node 610 were already a member tothe multicast group, then the node 610 would have already sent asubscription message into the first network for the multicast group. Thesubscription message would have been received by the node 608 andforwarded up to the root node 606 to form part of the PST in the firstnetwork. The rule used to facilitate this is to have a member (normal orconscripted) that is able to communicate with an adjacent network, senda subscription message in the member's network and the adjacent networkwhen the node becomes the member.

If the condition (i) and the condition (ii) are false (e.g., neither ofthose nodes is a member), the root node 606 proceeds to performoperation 640 in FIG. 6B. Here, the selected node is a non-member nodeto the multicast group.

At 640, the root node 606 may select a node to bridge communicationbetween the first network and the second network for a multicast group.The root node 606 may select a node of the first network that haspreviously communicated, or is otherwise able to communicate, with anode of the second network. The node may be selected based on a varietyof information that is available to the root node 606. For example, theroot node 606 may select a node within the first network that is closestto a member of the multicast group and that is within communicationrange of a node of the second network. In another example, the root nodeselects a node to provide the least routing cost between members of themulticast group and the node acting as the bridge (for example. thelowest number of transmissions to route data to members of the multicastgroup, or other measure of routing cost). In some instances, the samenode is selected for different multicast groups, while in otherinstances separate nodes are selected for different multicast groups. Toillustrate, a node that is currently acting as a bridge between networksfor a first multicast group, may be selected to act as a bridge betweenthose networks for a second multicast group.

At 642, the root node 606 sends a message to bridge communicationbetween the first network and the second network for the multicastgroup. In this example, the bridge node 608 is selected to bridgecommunication, and thus, the message is sent to this node. At 644, thebridge node 608 receives the message from the root node 606. In someinstances, the message is sent in a DIO communication, while in otherinstances the message is sent in other formats.

At 646, the bridge node 608 is configured to bridge communicationbetween the first network and the second network for the multicastgroup. In many instances, the operation 646 may include configuring thebridge node 608 to act as a virtual member of the multicast group. Insuch instances, the message sent at operation 642 instructs the bridgenode 608 to become a virtual member of the multicast group.

To become a virtual member, the bridge node 608 may send, at 648, asubscription message to the root node 606 of the first network. Thesubscription message may be received at 650 by the root node 606 of thefirst network. In other words, the subscription message may be sentnode-by-node through the first network node(s) 612 to reach the rootnode 606. The subscription message may indicate that the bridge node 608is becoming a virtual member of the multicast group. In response toreceiving the subscription message indicating that the bridge node 608is joining the multicast group as a virtual member, the root node 606may update membership information for the multicast group at 652 (e.g.,add the bridge node 608 and/or a multicast identifier for the multicastgroup to the list of multicast groups for the first network). The bridgenode 608 may be flagged as a virtual member.

Additionally, to become the virtual member, the bridge node 608 maycommunicate with the node 610 of the second network via one or morenodes of the second network to form a communication bridge. As alsoillustrated at 648, this may include sending a subscription message tothe node 610 to indicate that the bridge node 608 is becoming a virtualmember of the multicast group. The subscription message may be receivedat 654 by the node 610 and forwarded on to the root node 604 of thesecond network. The subscription message may be sent node-by-nodethrough one or more nodes of the second network to reach the root node604 of the second network. The root node 604 may receive thesubscription message at 656. In response to receiving the subscriptionmessage indicating that the bridge node 608 is joining the multicastgroup as a virtual member, the root node 604 may update membershipinformation for the multicast group at 658 (e.g., add the bridge node608 and/or a multicast identifier for the multicast group to the list ofmulticast groups for the second network). The bridge node 608 may beflagged as a virtual member.

In some instances, the subscription message sent at 648 is sent in a DAOcommunication, while in other instances the subscription message is sentin other formats.

Sending the subscription message up the first network and/or up thesecond network may cause a portion of a PST to be formed for themulticast group. For example, one or more messages may be sent to nodesin the first network and/or the second network to disable a pruningstate and/or otherwise configure nodes so that the bridge node 608receives multicast data for the multicast group. The PST may facilitatethe distribution of multicast data for the multicast group between thefirst network and the second network.

In general, a virtual member of a multicast group performs operationslike a member of the multicast group, but without processing multicastdata. For example, the virtual member may receive multicast data for themulticast group in a similar fashion as if it were an actual member ofthe multicast group. The virtual member may also forward on themulticast data as needed (e.g., based on a PST structure). A virtualmember does not usually process multicast data (e.g., at an applicationlayer), but merely passes the multicast data on to another node.

If the bridge node 608 ever becomes an actual member of the multicastgroup, the bridge node 608 transmits a normal subscription messageindicating membership in the multicast group. The subscription messagemay traverse each of the first and second networks to reach therespective root nodes. The root node 606 and the root node 604 mayremove the designation of the bridge node 608 as a virtual member andlist the bridge node 608 as a member.

Although the example of FIGS. 6A-6B discuss the bridge node 608 of thefirst network becoming a virtual member, in other instances the bridgenode 608 may communicate with the node 610 of the second network tocause the node 610 to become the virtual member. Here, the node 610 maybe implemented as a “bridge node” or “conscript,” instead of the bridgenode 608.

At some point after the bridge node 608 becomes a virtual member, and aPST is formed with the bridge node 608, multicast data for the multicastgroup may be distributed to members of the multicast group. In oneexample, multicast data originates in the first network and is sent fromthe first network node(s) 612. The bridge node 608 receives themulticast data at 660, and then forwards the multicast data on to thesecond network by sending it to the node 610, at 662. The multicast datamay be received by the node 610 at 664. The multicast data may then bedistributed through the second network according to the PST. In anotherexample, multicast data that originates in the second network is sent,at 666, by the node 610 to the bridge node 608. The bridge node 608receives the multicast data at 660 and forwards the multicast data on tothe first network of nodes at 662 according to the PST. This may allowmulticast data to be distributed to members of both networks.

Example Messages

FIG. 7 illustrates an example portion of a subscription message 700 toadvertise that a node is a member of a multicast group. The portion ofthe subscription message 700 may form a Destination Advertisement Object(DAO) Base Object of a DAO message (e.g., ICMPv6 message). That is, thesubscription message may correspond to the DAO message used in a RoutingProtocol for Low Power and Lossy Networks (RPL) protocol, while theportion of the subscription message 700 may correspond to the DAO BaseObject. However, the subscription message may take other forms and/or beimplemented in other protocols.

A DAO message may generally be transmitted hop-by-hop to allow nodes ina network to have information about their sub-trees and/or optimizepoint-to-point routing. In many instances, a DAO message is transmittedby a node up the network to join the node to a root node and/or tomaintain an existing relationship with a root node.

In this example, the portion of the DAO message 700 has a Unicast Targetoption 702, which carries an address (e.g., global unicast IPv6 address)of a given target. The Unicast Target option 702 identifies the nodethat originated the DAO message, such as the node that is subscribing toa multicast group.

The portion of the DAO message 700 also has a Multicast Target option704 set to a multicast group address associated with a multicast groupto which the node is subscribing. As such, the Multicast Target Optionmay indicate the multicast group to which the node is subscribing. Toillustrate, the Multicast Target option 702 may carry a multicastaddress (e.g., IPv6 address) to which a concerned unicast targetsubscribes.

As illustrated, the portion of the DAO message 700 has a TransitInformation option 706, which carries the unicast address (e.g., globalIPv6 address) of a DAO parent of the concerned unicast target. Further,the portion of the DAO message 700 includes one or more Pad options 708to ensure that a total length of a header is a multiple of 8 bytes.

Although illustrated in a particular order, any of the options 702-708may be arranged differently. Further, any of the options 702-708 may beused in other types of messages and/or omitted from the DAO message.

The options 702-706 may be repeated for each RPL Unicast Targetdescribed in the DAO. Furthermore, the option 706 may be repeated foreach DAO parent of the concerned unicast target. Further, the MulticastTarget option 702 may occur N times (where N is an integer greater thanor equal to zero and corresponds to the number of multicast groups ofwhich the node is a member). For example, if the node is a member ofmultiple multicast groups, the multicast address (i.e., the multicastTarget option 702) of each group would be included, one after the other,in the DAO.

The information in the portion of the DAO message 700 may be inspectedas the DAO message is transmitted throughout a network (e.g., at eachhop). For example, the Unicast Target option 702 and the MulticastTarget option 704 may be inspected to identify a multicast group towhich the node is subscribing. This information may be used to update adata structure indicating membership of the node in the multicast group.

FIG. 8 illustrates an example portion of a message 800 to instruct anode to disable or enable a pruning state. Such message is oftenreferred as a MinP message. The MinP 800 may correspond to a DODAGInformation Object (DIO) message used in the RPL protocol, while theportion of the MinP message 800 corresponds to a new option that isprovided within a DIO message. Such option is also referred to as aPST-MinP option. The example PST-MinP option 800 is just one of manyforms of implementation. Here, the example PST-MinP option 800 is for aType-Length-Value (TLV) structure. However, a variety of otherstructures and/or fields may be used.

The PST-MinP option 800 may identify one or more multicast groups forwhich pruning should be disabled. Here, the PST-MinP option 800 includesa type field 802, which indicates a type of the option (e.g., that theoption is a PST-MinP option), and a length field 804, which indicates alength of the PST-MinP option 800 (excluding the type field 802 and thelength field 804). The PST-MinP option 800 also includes a flags field806 that is part of a TLV structure, and a number of groups field 808that indicates a number of multicast groups advertised in this option.Further, the PST-MinP option 800 includes a multicast group addressfield 810 that includes a multicast address of each advertised group. Inother words, the multicast group address field 810 declares one or moremulticast group addresses for which child nodes of a transmitting nodemust disable a pruning state. As such, the multicast group address field810 identifies multicast groups for which to disable a pruning state.

Although illustrated in a particular order, any of the fields 802-810may be arranged differently. Further, any of the fields 802-810 may beused in other types of messages and/or omitted from the DIO message.

In some instances, a DIO message with the PST-MinP option 800 istransmitted as a link-local multicast packet. The DIO message isprocessed if received from a preferred parent. To illustrate, a DIOmessage may be sent as a one-hop multicast transmission and filtered byrecipients to only be processed if received from a PST parent.

The information in the PST-MinP option 800 may be processed to update apruning state. For example, a node that receives the PST-MinP option 800in a message may analyze the multicast group address field 810 toidentify a multicast group for which to disable the pruning state.

Example Processes

FIGS. 9, 10, and 11 illustrate example processes 900, 1000, and 1100 foremploying the techniques discussed herein. The processes 900, 1000, and1100 may be performed by any type of device, such as the serviceprovider 106, the node 200, or any other device.

The processes 900, 1000, and 1100 (as well as each process describedherein) are illustrated as logical flow graphs, each operation of whichrepresents a sequence of operations that can be implemented in hardware,software, or a combination thereof. In the context of software, theoperations represent computer-readable instructions stored on one ormore computer-readable storage media that, when executed by one or moreprocessors, perform the recited operations. Generally, computer-readableinstructions include routines, programs, objects, components, datastructures, and the like that perform particular functions or implementparticular abstract data types. In some contexts of hardware, theoperations may be implemented (e.g., performed) in whole or in part byhardware logic components. For example, and without limitation,illustrative types of hardware logic components that can be used includeField-programmable Gate Arrays (FPGAs), Application-specific IntegratedCircuits (ASICs), Application-specific Standard Products (ASSPs),System-on-a-chip systems (SOCs), Complex Programmable Logic Devices(CPLDs), etc. The order in which the operations are described is notintended to be construed as a limitation, and any number of thedescribed operations can be combined in any order and/or in parallel toimplement the process. Further, any number of the described operationsmay be omitted.

FIG. 9 illustrates the example process 900 to bridge communicationbetween networks with a member node acting as a bridge.

At 902, a first node of a first network may communicate with a node of asecond network. This may include sending and/or receiving any number ofcommunications to discover each other. In some instances, the node ofthe second network is a member of a multicast group, while in otherinstances the node is not.

At 904, the first node may determine that the first node is able tocommunicate with the node of the second network. This may be based onthe communication at the operation 902.

At 906, the first node may send a subscription message indicating thatthe first node is a member of a multicast group. The message may be sentto the node of the second network, a node of the first network, and/orany other node that is within communication range. The subscriptionmessage may traverse the first network and/or the second network toreach the respective root node. In some instances, the operation 906 isbased on the determining that the first node is able to communicate withthe node of the second network.

At 908, the first node may receive a message instructing the first nodeto disable a pruning state. The message may be received from a node ofthe first network, such as a parent node, and/or received from a node ofthe second network.

At 910, the first node may disable the pruning state based on thereceipt of the message at operation 908.

At 912, the first node may forward data between the first network andthe second network for the multicast group. The data may be destined formembers of the multicast group. In some instances, the forwardingincludes receiving the data from a node of the first network and sendingthe data to a node of the second network. In other instances, theforwarding includes receiving the data from a node of the second networkand sending the data to a node of the first network. In some examples,the forwarding may be based on determining that the pruning state isdisabled.

FIG. 10 illustrates the example process 1000 to bridge communicationbetween networks with a member in an adjacent network.

At 1002, a first node of a first network may communicate with a node ofa second network. This may include sending and/or receiving any numberof communications to discover each other. In some instances, the firstnode is a member of a multicast group, while in other instances thefirst node is not.

At 1004, the first node may receive a subscription message indicatingthat the node of the second network is a member of the multicast group.The subscription message may be received from the node of the secondnetwork.

At 1006, the first node may send the subscription message within thefirst network to reach a root node of the first network. For example,the first node may send the subscription message to a parent node oranother node that is able to hear the first node. The subscriptionmessage may traverse the first network to reach a root node.

At 1008, the first node may receive a message instructing the first nodeto disable a pruning state. The message may be received from a node ofthe first network, such as a parent node, and/or received from a node ofthe second network.

At 1010, the first node may disable the pruning state based on thereceipt of the message at 1008.

At 1012, the first node may forward data between the first network andthe second network for the multicast group. The data may be destined formembers of the multicast group. In some instances, the forwardingincludes receiving the data from a node of the first network and sendingthe data to the node of the second network. In other instances, theforwarding includes receiving the data from the node of the secondnetwork and sending the data to a node of the first network. In someexamples, the forwarding may be based on determining that the pruningstate is disabled.

FIG. 11 illustrates the example process 1100 at a root node to bridgecommunication between networks.

At 1102, a root node of a first network may receive a subscriptionmessage indicating that a node of the first network is subscribing to amulticast group (e.g., is a member of the multicast group). The rootnode may receive subscription messages from any number of nodes of thefirst network indicating that the nodes are members of the multicastgroup. Additionally, or alternatively, the root node may receive anynumber of subscription messages indicating that a node of a secondnetwork is a member of the multicast group. For example, a node of thesecond network that is able to communicate with a node of the firstnetwork may send a subscription message to the node of the firstnetwork. The subscription message may traverse the first network toreach the root node.

At 1104, the root node may send, to a central agent, informationindicating that the first network includes a member of a multicast groupand/or that the first network is able to communicate with a secondnetwork. The information may be based on a subscription message(s)received at 1102. The information that is sent to the central agent mayinclude a list of multicast groups that have members in the firstnetwork and/or a list of networks that have communicated with the firstnetwork.

At 1106, the root node may receive, from the central agent, a messagerequesting that the root node bridge communication between the firstnetwork and the second network to allow distribution of data to membersof the multicast group. The message may include a list of networks thatare adjacent to the first network and that are requested to connect toin bridging communication for the multicast group.

At 1108, the root node may determine if (i) a node of the second networkthat is able to communicate with the first network is a member of themulticast group, and/or (ii) a node of the first network that is able tocommunicate with the second network is a member of the multicast group.

If the condition (i) and/or the condition (ii) is true, then the process1100 may proceed to 1110. If not, then the process 1100 may proceed to1112.

At 1110, the root node may refrain from selecting a node to bridgecommunication between the first network and the second network. Here, abridge has already been established by the member node of the secondnetwork that is able to communicate with the first network or the membernode of the first network that is able to communicate with the secondnetwork.

At 1112, the root node may select a node to bridge communication betweenthe first network and the second network. In one example, the operation1112 may perform the processing of operation 640 of FIG. 6B and continueto 642 and so on. In another example, other processing may be performedto select a node to bridge communication.

1. One or more non-transitory computer-readable media storing executableinstructions that, when executed by one or more processors of a centralagent, cause the one or more processors to perform operationscomprising: receiving, from a first root node of a first network,information indicating that the first network includes a member of amulticast group; receiving, from a second root node of a second network,information indicating that the second network includes a member of themulticast group; based at least in part on the information from thefirst root node and the information from the second root node,determining that the first network and the second network each have atleast one member of the multicast group; determining to bridgecommunication between the first network and the second network to allowdistribution of data to members of the multicast group; and sending amessage requesting that communication be bridged between the firstnetwork and the second network to allow distribution of data to themembers of the multicast group.
 2. The one or more non-transitorycomputer-readable media of claim 1, wherein the information from thesecond root node indicates that a node of the first network hascommunicated with a node of the second network, the operations furthercomprising: determining that the first network is adjacent to the secondnetwork; wherein the sending the message comprises sending the messageto at least one of the first root node or the second root node to causea node of the first network or a node of the second network to bridgecommunication between the first network and the second network.
 3. Theone or more non-transitory computer-readable media of claim 1, whereinthe operations further comprise: determining that the first network isnot adjacent to the second network; and determining that a third networkis positioned adjacent to the first network and adjacent to the secondnetwork; wherein the determining to bridge communication between thefirst network and the second network comprises determining to use thethird network to bridge communication between the first network and thesecond network; and wherein the sending the message comprises sendingthe message to at least one of the first root node, the second rootnode, or a third root node of the third network.
 4. The one or morenon-transitory computer-readable media of claim 1, wherein: theinformation from the first root node includes a list of multicast groupsthat have members in the first network and a list of networks that havecommunicated with the first network; and the information from the secondroot node includes a list of multicast groups that have members in thesecond network and a list of networks that have communicated with thesecond network.
 5. The one or more non-transitory computer-readablemedia of claim 4, wherein the operations further comprise: determining alist of networks that include at least one member of the multicastgroup, the list of networks including the first network and the secondnetwork; determining a plurality of networks that are needed to bridgecommunication to the list of networks that include at least one memberof the multicast group, the plurality of networks including the firstnetwork and the second network, each network of the plurality ofnetworks being adjacent to at least one other network of the pluralityof networks; wherein the sending the message comprises sending themessage to a root node of a particular network of the plurality ofnetworks, the message requesting that communication be bridged betweenthe particular network and a network, from among the plurality ofnetworks, that is adjacent to the particular network.
 6. The one or morenon-transitory computer-readable media of claim 5, wherein the pluralityof networks include an intermediary network that does not have a memberin the multicast group.
 7. A root node of a first network, the root nodecomprising: one or more processors; and memory communicatively coupledto the one or more processors, the memory storing one or moreinstructions that, when executed by the one or more processors, causethe one or more processors to perform operations comprising: determiningthat the first network includes a member of a multicast group;determining that a node of the first network able to communicate with anode of a second network; sending, to a central agent, informationindicating that the first network includes a member of the multicastgroup and that the first network is able to communicate with the secondnetwork; receiving, from the central agent, a message requesting thatthe root node bridge communication between the first network and thesecond network to allow distribution of data to members of the multicastgroup; selecting the node of the first network that is able tocommunicate with the node of the second network to bridge communicationbetween the first network and the second network for the multicastgroup; and sending, via the first network, a message instructing theselected node to bridge communication between the first network and thesecond network for the multicast group.
 8. The root node of claim 7,wherein the information that is sent to the central agent includes alist of multicast groups that have members in the first network and alist of networks that have communicated with the first network.
 9. Theroot node of claim 7, wherein the message from the central agentincludes a list of networks that are adjacent to the first network andthat are requested to connect to in bridging communication for themulticast group, the list of networks including the second network. 10.The root node of claim 7, wherein the message instructing the selectednode to bridge communication between the first network and the secondnetwork instructs the selected node to become a virtual member of themulticast group.
 11. The root node of claim 7, wherein selecting thenode of the first network to bridge communication between the firstnetwork and the second network for the multicast group comprisesselecting the node of the first network based on at least one of aproximity of the node of the first network to a member of the multicastgroup or a routing cost between members of the multicast group and thenode of the first network.
 12. The root node of claim 7, wherein theoperations further comprise: receiving a subscription message indicatingthat the selected node is subscribing as a virtual member to themulticast group; and updating membership information for the firstnetwork to indicate that the selected node is the virtual member of themulticast group.
 13. The root node of claim 7, wherein the operationsfurther comprise: determining that the node of the first network thathas communicated with the node of the second network is currently actingas a bridge between the first network and the second network for anothermulticast group; wherein the selecting is based at least in part on thedetermining that the node of the first network that has communicatedwith the node of the second network is currently acting as the bridgebetween the first network and the second network for the other multicastgroup.
 14. A first node of a first network, the first node comprising:one or more processors; and memory communicatively coupled to the one ormore processors, the memory storing one or more instructions that, whenexecuted by the one or more processors, cause the one or more processorsto perform operations comprising: communicating with a second node of asecond network; sending, to the second node, a first message destinedfor a root node of the second network, the first message indicating thatthe first node is a member of the first network; receiving a secondmessage instructing the first node to bridge communication between thefirst network and the second network for a multicast group; andconfiguring the first node to bridge communication between the firstnetwork and the second network for the multicast group.
 15. The firstnode of the first network of claim 14, wherein the configuring comprisessending a subscription message destined for a root node of the firstnetwork, the subscription message indicating that the first node is avirtual member of the multicast group.
 16. The first node of the firstnetwork of claim 14, wherein the configuring comprises sending asubscription message destined for the root node of the second network,the subscription message indicating that the first node is a virtualmember or a member of the multicast group.
 17. The first node of thefirst network of claim 14, wherein the operations further comprise:receiving, from a node of the first network, data for the multicastgroup; and forwarding the data to the second node to distribute the datato a member of the multicast group that is part of the second network.18. The first node of the first network of claim 14, wherein theoperations further comprise: receiving, from the second node of thesecond network, data for the multicast group; and forwarding the data toa node of the first network to distribute the multicast data to a memberof the multicast group that is part of the first network.
 19. The firstnode of the first network of claim 14, wherein the first network isimplemented as a first Destination Oriented Directed Acyclic Graph(DODAG).
 20. The first node of the first network of claim 14, whereinthe first node comprises a Limited Function Device (LFD).